1. Field of the Invention
The present invention is directed generally to devices for and methods of locating a catheter inside a body and more particularly to devices for and methods of locating the tip of a central venous catheter inside the superior vena cava, right atrium, and/or right ventricle using information obtained from an electrocardiogram.
2. Description of the Related Art
Central venous catheters (“CVC”) include any catheter designed to utilize the central veins (e.g., subclavian and superior vena cava) or right sided cardiac chambers for the delivery and/or withdrawal of blood, blood products, therapeutic agents, and/or diagnostic agents. CVCs also include catheters inserted into the central veins or right sided cardiac chambers for the acquisition of hemodynamic data. Standard central venous catheters for intravenous access, dialysis catheters, percutaneously introduced central catheters (“PICC” lines), and right heart (“Swan-Ganz™”) catheters are examples of CVCs.
The standard of care for placing a CVC (other than right heart catheters which generally terminate in the pulmonary artery) dictates that the tip of the CVC lie just above and not inside the right atrium. In fact, in 1989, the Food and Drug Administration issued a warning citing an increased risk of perforation of the right atrium, clot formation, and arrhythmias among other potential complications resulting from the tip of the CVC being placed inside the right atrium.
While CVCs have been used for many years, determining the position of the tip of the CVC has always been problematic. Currently, a chest x-ray is used to determine the position of the tip of the CVC. Because CVC may be a radiopaque and/or include radiopaque materials, the CVC is visible on an x-ray. However, this method has several drawbacks. For example, obtaining a chest x-ray is labor intensive and expensive. In recent years, CVCs, which were traditionally placed in a hospital in-patient setting, are being placed in an outpatient setting more frequently. In an outpatient setting, obtaining a chest x-ray to determine the position of the tip of the CVC can be very cumbersome and may not be obtained in a timely manner. Therefore, using a chest x-ray to determine the position of the tip of the CVC may introduce a considerable delay, prolonging the procedure. Generally, the operator will leave the patient to perform other duties while the x-ray is processed. If the tip is improperly placed, the operator must return to the patient's bedside to reposition the CVC. To reposition the CVC, the operator must open the sterile dressing, cut the sutures, re-suture, and redress the wound, all of which potentially expose the patient to discomfort and infection.
Recently, navigational systems principally used to guide peripherally placed lines have become available. Based upon the detection of magnetic fields between a stylet tip and a detector, these systems assume (and depend upon) a relationship between surface landmarks and anatomic locations. Unfortunately, these systems cannot be used to determine the location of the tip of a CVC with sufficient accuracy because the relationship between surface landmarks and anatomic locations is highly variable from one patient to another.
In addition to the need to know where the tip is during initial placement, the CVC may migrate or otherwise move after the initial placement and require re-positioning. Therefore, the operator must monitor or periodically reevaluate the location of the tip.
An electrocardiogram (“ECG”) measures electrical potential changes occurring in the heart. Referring to FIGS. 1A-1C, the ECG measurements may be visualized or displayed as an ECG trace, which includes ECG waveforms. As is appreciated by those of ordinary skill in the art, ECG waveforms are divided into portions that include a QRS complex portion and a P wave portion in addition to other wave portions. The QRS complex corresponds to the depolarization of the ventricular muscle. The P wave portion of the ECG waveforms represents atrial muscle depolarization: the first half is attributable to the right atrium and the second half to the left atrium. Under normal circumstances, atrial muscle depolarization is initiated by a release of an excitatory signal from the sino-atrial (“SA”) node, a specialized strip of tissue located at the juncture of the superior vena cava (“SVC”) and right atrium.
As is appreciated by those of ordinary skill in the art, an ECG may be obtained using different electrode configurations. For example, a standard configuration referred to as “Lead II” may used. In a bipolar Lead II configuration, one of the electrodes (the cathode) is attached to the left leg and the other electrode (the anode) is attached to the right shoulder. As is appreciated by those of ordinary skill in the art, using a different configuration could change the polarity and/or the shape of the P wave. Other standard bipolar configurations include a bipolar Lead I configuration where the cathode is attached to the left shoulder and the anode is attached to the right shoulder and a bipolar Lead III configuration where the cathode is attached to the left leg and the anode is attached to the right shoulder.
The waveforms depicted in FIGS. 1A-1C and 2B were obtained using the anode of a standardized bipolar ECG Lead II configuration attached to the right shoulder and the tip of the CVC as the cathode. While technically this configuration is not a standard Lead II configuration, the trace produced by the electrodes 114A and 114B may be displayed on a standard ECG monitor using the monitor's circuitry to display the trace as a bipolar Lead II trace.
Techniques of using ECG waveforms to locate the tip of a CVC have been available since the 1940's. Some of these prior art devices construct an intravascular ECG trace by placing an electrode near the tip of the CVC and using that electrode to measure the voltage near the tip of the CVC relative to a surface electrode(s) and/or a second electrode spaced from the first.
These techniques have shown that both the magnitude and shape of the P wave change depending upon the positioning or location of the electrode attached to the tip of the CVC. Referring to FIGS. 1A and 1B, two exemplary ECG traces are provided for illustrative purposes.
FIG. 1A is an ECG trace made when the electrode attached to the tip of the CVC is in the proximal SVC. This tip location corresponds to position “1” depicted in FIG. 2A. The portion of the ECG trace corresponding to an exemplary P wave produced when the electrode attached to the tip is located in position “1” is labeled “P1.”
FIG. 1B is an ECG trace made when the electrode attached to the tip of the CVC is approaching the SA node and stops at a location adjacent to the SA node. These tip locations correspond to moving the tip from a position “2” to position “3” depicted in FIG. 2A. The portion of the ECG trace corresponding to an exemplary P wave produced when the electrode attached to the tip is approaching the SA node is labeled “P2” and the portion of the ECG trace corresponding to an exemplary P wave produced when the electrode attached to the tip is located adjacent to the SA node is labeled “P3.”
Normally as the electrode attached to the tip of the CVC moves from the proximal SVC (position “1”) toward the SA node (position “3”), the maximum value of the absolute value of the voltage of the P wave increases dramatically. When the electrode attached to the tip of the CVC is adjacent to the SA node (position “3”), the voltage of the P wave (please see “P3” of FIG. 1B) reaches a maximum value that is more than twice the value experienced in the proximal SVC and may be as large as eight times the voltage in the proximal SVC. When this occurs, the tip of the CVC is considered to have entered into the right atrium. Because the magnitude of the P wave more than doubles when the electrode attached to the tip of the CVC is adjacent to the SA node, this information may be used to place the tip of the CVC within a few centimeters (e.g., about 1 cm to about 2 cm) proximal to the SA node. Additionally, as the electrode attached to the tip of the CVC moves from the proximal SVC toward the right atrium, the shape of the P wave changes from a “u” shape (FIG. 1A) to a spike-like shape (FIG. 1B).
Referring to FIG. 2B, another exemplary illustration of the P wave portion of the ECG trace produced when the electrode attached to the tip of the CVC is located at positions 1-5 depicted in FIG. 2A is provided. The P wave portions of the ECG traces of FIG. 2B are labeled with the letter “P” and occur between the vertical dashed lines. Each of the exemplary traces is numbered to correspond to positions “1” through “5.” Therefore, the ECG trace “1” was produced when the electrode attached to the tip was located in the proximal SVC. The trace “2” was produced when the electrode attached to the tip was in position “2” (distal SVC). The trace “3” was produced when the electrode attached to the tip was adjacent to the SA node.
As the electrode attached to the tip of the CVC is advanced further into the right atrium, the polarity of the P wave “P” changes from predominantly negative near the top of the right atrium (position “3”) to isoelectric (i.e., half has a positive polarity and half has a negative polarity) near the middle of the right atrium (position “4”) to almost entirely positive at the bottom of the right atrium (position “5”). These changes in the P wave “P” are illustrated in traces “3” through “5.”
FIG. 1C is an ECG trace made when the electrode attached to the tip of the CVC is in the right ventricle. The portion of the ECG trace corresponding to an exemplary P wave produced when the electrode attached to the tip is labeled “P6.” When the electrode attached to the tip of the CVC is advanced into the right ventricle, the maximum magnitude of the absolute value of the P wave “P6” approximates the maximum magnitude of the absolute value of the P wave “P1” when the electrode attached to the tip of the CVC was inside the proximal SVC above the SA node (i.e., located at position “1”). However, the polarity of the first half of P wave “P6,” which corresponds to the right atrium, is opposite.
The first technique developed for viewing the ECG waveform during the insertion of a CVC used a column of saline disposed within a hollow tube or lumen longitudinally traversing the CVC. The column of saline provides a conductive medium. Saline was inserted into the lumen by a saline filled syringe with a metal needle. The needle of the syringe remained within the entrance to the lumen or port in contact with the column of saline after the lumen was filled. One end of a double-sided alligator clip was attached to the needle and the other end was attached to an ECG lead, which in turn was attached to an ECG monitor. By using the saline solution filled CVC as a unipolar electrode and a second virtual electrode generated by ECG software from three surface electrodes, an intravascular ECG was obtained. The operator would adjust the position of the tip of the CVC based on the magnitude and shape of the P wave displayed by the ECG monitor.
Subsequently, this technique was modified by substituting an Arrow-Johans adapter for the metal needle. The Arrow-Johans adapter is a standard tubing connector with an embedded conductive ECG eyelet. The Arrow-Johans adapter may be placed in line with any conventional CVC. In a closed system, the tubing and CVC may be filled with saline, i.e., a conductive medium, and the CVC used as a unipolar electrode in conjunction with surface electrodes and a standard ECG monitor. The ECG eyelet is placed in contact with the saline in the lumen of the CVC. One end of the ECG lead is attached to the ECG eyelet and the other end to the ECG monitor for displaying the intravascular ECG waveforms. Because the system must be closed to prevent the saline from leaking out, this system works best after the guide wire used to thread the CVC forward has been withdrawn, i.e., after placement has been completed. Therefore, although the catheter may be withdrawn after initial placement, it may not be advanced into proper position.
B. Braun introduced its Certofix catheter to be used in conjunction with its CERTODYN adapter. In this system, a patch lead with two ends has an alligator clip connected to one end. The alligator clip is clipped to the CVC guide wire. The other end of the patch lead includes a connector that is plugged into the CERTODYN adapter. The ECG may be obtained during placement and the catheter may be advanced or withdrawn as desired. However, the CERTODYN adapter has many moving parts and is not sterile, making the procedure cumbersome to perform and the operative field more congested. Additionally, the sterile field may become contaminated by the non-sterile equipment.
The Alphacard, manufactured by B. Braun, merges the Arrow-Johans adapter and the CERTODYN adapter. The Alphacard consists of a saline filled syringe (used to flush the CVC with saline) and a connector to the CERTODYN. The Alphacard is used to obtain a ‘snapshot’ of the ECG trace from the saline column. If an atrial spike is seen in the ECG trace, the CVC is withdrawn.
With respect to all of these prior art methods of using an ECG trace to place the tip of the CVC, some degree of expertise is required to interpret the P waves measured because the user must advance the guide wire slowly and watch for changes in the P wave. If the catheter is inserted too far too quickly and the changes to the P wave go unnoticed (i.e., the operator fails to notice the increase or spike in the voltage experienced when the electrode attached to the tip is in the right atrium), the operator may mistakenly believe the tip is in the SVC when, in fact, the tip is in the right ventricle. If this occurs, advancing the tip may injure the patient.
U.S. Pat. Nos. 5,078,678 and 5,121,750 both issued to Katims teach a method of using the P wave portion of an ECG trace to guide placement of the tip of the CVC. The CVC includes two empty lumens into which a transmission line is fed or an electrolyte is added. Each of the lumens has a distal exit aperture located near the tip of the CVC. The two exit apertures are spaced from one another. In this manner, two spaced apart electrodes or a single anode/cathode pair are constructed near the tip of the CVC. The voltage or potential of one of the electrodes relative to the other varies depending upon the placement of the electrodes. The voltage of the electrodes is conducted to a catheter monitoring system. The catheter monitoring system detects increases and decreases in the voltage of the P wave. The voltage increases as the electrodes approach the SA node and decrease as the electrodes move away from the SA node. Based on whether the voltage is increasing or decreasing, the operator is instructed by messages on a screen to advance or withdraw the CVC.
While Katims teaches a method of locating the tip of a CVC relative to the SA node, Katims relies on advancing or withdrawing the CVC and observing the changes of the P wave. Katims does not disclose a method of determining the location of the tip of the CVC based on a single stationary position. Unless the entire insertion procedure is monitored carefully, the method cannot determine the position of the tip of the CVC. Further, the Katims method may be unsuitable for determining the location of a previously positioned stationary tip.
Other devices such as Bard's Zucker, Myler, Gorlin, and CVP/Pacing Lumen Electrode Catheters are designed primarily to pace. These devices include a pair of electrodes at their tip that are permanently installed and designed to contact the endocardial lining. These devices include a lumen, which may be used to deliver and/or withdraw medications or fluids as well as for pressure monitoring. These leads are not designed for tip location and do not include multi-lumen capability.
A method of obtaining an intravascular ECG for the purposes of placing a temporary pacing wire was described in U.S. Pat. No. 5,666,958 issued to Rothenberg et al. Rothenberg et al. discloses a bipolar pacing wire having a distal electrode. The distal electrode serves as a unipolar electrode when the pacing wire is inserted into the chambers of the heart. The pacing wire is connected to a bedside monitor through a specialized connector for the purposes of displaying the ECG waveforms detected by the distal electrode.
Given the volume of CVCs placed yearly and the increasing demand particularly for PICC lines (devices that permit the delivery of intravenous therapeutic agents in the outpatient setting, avoiding the need for hospitalization) a great need exists for methods and devices related to locating the tip of a CVC. Particularly, devices and methods are needed that are capable of determining the location of the tip before the operator leaves the bedside of the patient. Further, a method of determining the location (SVC, right atrium, or right ventricle) of the tip from a single data point rather than from a series of data points collected as the catheter is moved may be advantageous. Such a system may be helpful during initial placement and/or repositioning. A need also exists for a device for or a method of interpreting the ECG waveforms that does not require specialized expertise. Methods and devices that avoid the need for hospital and x-ray facilities are also desirable. A need also exists for devices and methods related to determining the position of the tip of the CVC that are less expensive, expose patients to fewer risks, and/or are less cumbersome than the x-ray method currently in use.